Interpretive Summary: E. coli O157:H7 is a harmful bacteria that lives in ruminant animals (for example, deer, cattle and sheep). E. coli O157:H7 sickens over 76,000 Americans each year via foodborne illness. Previously we have shown that a chemical called chlorate kills E. coli. Sheep experimentally infected with E. coli O157:H7 were treated with sodium chlorate in drinking water. Chlorate reduced E. coli, total coliform, and E. coli O157:H7 populations throughout the gut. This is important to the animal industry because treatment with sodium chlorate could be a new way to reduce the numbers of harmful bacteria like pathogenic E. coli in the animal gut, resulting in reduced human foodborne illness.

Technical Abstract:
Ruminant animals are a natural reservoir of the food-borne pathogen Escherichia coli O157:H7. Some food borne pathogens (e.g., E. coli) are equipped with a nitrate reductase that co-metabolically reduces chlorate. The intracellular reduction of chlorate to chlorite kills bacteria equipped with nitrate reductase; however, bacteria that do not reduce nitrate are not affected by chlorate. Therefore it has been suggested that ruminants be supplemented with chlorate prior to shipment for slaughter in order to reduce food borne illnesses in human consumers. Sheep (n=14) were fed a high grain ration and were experimentally infected with E. coli O157:H7 at t=0h and were given drinking water supplemented with either 2.5 mM NaNO3 and 100 mM NaCl (Controls; n=7) or 2.5 mM NaNO3 and 100 mM NaClO3 (Chlorate-treated; n=7) at t=48h. Sodium chlorate was supplemented to sheep for 24 h; the population of E. coli O157:H7 was reduced (P < 0.05) from 10**2, 10**5 and 10**5 (CFU/g) in the rumen, cecum and rectum of control sheep (n=7), respectively to <10**1 CFU/g in each section of the gastrointestinal tract of chlorate-treated sheep (n=7). The number of sheep that were positive for E. coli O157:H7 was significantly reduced by chlorate treatment compared to controls. In a similar fashion, total E. coli and coliforms were also reduced (P < 0.05) in all three compartments of the intestinal tract of chlorate treated sheep compared with controls. Intestinal pH, total VFA production and the A:P ratio were unaffected by chlorate supplementation compared to controls. Based on these results it appears that sodium chlorate can be an effective method to reduce E. coli O157:H7 populations in ruminant animals immediately prior to slaughter.